1. Field of the Disclosure
The disclosure relates to a reflective electrode and a compound semiconductor light emitting device having the same, and more particularly, to a reflective electrode having low contact resistance, high reflectance, and improved electric conductivity and a compound semiconductor light emitting device having the same.
2. Description of the Related Art
Compound semiconductor light emitting devices can convert an electrical signal to light using a characteristic of a compound semiconductor. Recently, laser light of a semiconductor laser diode, such as a light emitting diode (LED) or a laser diode (LD), is practically used fields, such as optical communications, multiple communications, and space communications. A semiconductor laser is widely used as a light source for transmitting data, recording data, or reading data in a device such as compact disc players (CDP) or digital versatile disc players (DVDP), or optical communications.
The compound semiconductor light emitting device can be classified as a top-emitting light emitting diode (TLED) and a flip-chip light emitting diodes (FCLED) according to the direction of light emission.
The TLED has a light emitting structure in which light is emitted through a p-type electrode that forms an ohmic contact with the p-type compound semiconductor layer. The p-type electrode has a structure of sequentially stacked of a nickel (Ni) layer and a gold (Au) layer on the p-type compound semiconductor layer. However, the p-type electrode formed of Ni layer/Au layer is semitransparent, and a TLED to which the p-type electrode is applied has a low light utilization efficiency and low brightness.
The FCLED has a light emitting structure in which light generated from an active layer is reflected by a reflective electrode formed on the p-type compound semiconductor layer and the reflected light is emitted through a substrate. The reflective electrode can be formed of a material having a superior light reflection characteristic, such as silver (Ag), aluminum (Al), or rhodium (Rh). A FCLED to which the reflective electrode is applied has high light utilization efficiency and high brightness. However, the reflective electrode has high contact resistance on the p-type compound semiconductor layer. Therefore, there are drawbacks in that the FCLED to which the reflective electrode is applied has a short life time and the characteristic of the FCLED is unstable.
To solve this problem, research related to electrode materials that have low contact resistance and high reflectance and a structure of electrode has been performed.
International Publication No. WO 01/47038 A1 discloses a technique about a semiconductor light emitting device to which a reflective electrode is applied. In this disclosure, an ohmic contact layer is interposed between the reflective electrode and the p-type compound semiconductor layer, but the materials (Ti, Ni/Au etc.) for forming the ohmic contact layer have low light transmittance. Therefore, there is a need to improve the light utilization efficiency and brightness.